1. Field of the Invention
The invention relates to an electrochemical storage cell of the sodium and sulfur type with an anode space and a cathode space which are separated from each other via a cup-shaped solid electrolyte within which a safety container for receiving the sodium is arranged which is in communication with the interior of the solid electrolyte via a hole.
2. Description of the Prior Art
Such electrochemical storage cells are highly suited as energy sources. They find increasing use in the construction of storage batteries which are provided as the power supply of electric vehicles.
A specific example for these storage cells are those of the sodium and sulfur type which are rechargeable and have a solid electrolyte of beta-aluminum oxide which separates the anode space from the cathode space. It is an advantage of these storage cells that no secondary electrochemical reactions occur during charging. The reason for this is that only sodium ions can pass through the solid electrolyte. The current yield of such sodium/sulfur storage cells is therefore approximately 100%. In these electrochemical storage cells the ratio of energy content to the total weight of a storage cell is very large as compared with lead storage batteries, since the reactants are light and much energy is released in the electrochemical reactions.
U.S. Pat. No. 4,247,605 discloses an electrochemical storage cell of the sodium and sulfur type in which a safety container is arranged in the cup-shaped solid electrolyte. The safety container serves to receive the sodium. The dimensions of the safety container and the solid electrolyte are chosen to leave a coherent space between its outside surface and the inside surface of the solid electrolyte. This coherent space which extends all around serves as a safety gap and is filled with a material acting as capillaries. On the side facing the bottom of the solid electrolyte, the safety container is provided with a hole through which the sodium can pass into the solid electrolyte and in particular, into the safety gap. The capillary material contained in the safety gap is powder- or fiber-like. Since this material is arranged in the entire safety gap, especially in the region in which the hole of the safety container is located, this hole may, in the course of time, become clogged up by this capillary material. When clogging of the hole occurs, the outflow and possibly also a return of the sodium from and into the safety container is prevented, with operability of the storage cell limited severely or stopped altogether.